Approximately 30,000 traumatic brain injuries that require decompressive craniectomy (e.g., removal of a cranial bone flap) occur in the United States every year. Decompressive craniectomies are used to treat patients with massive brain swelling following either trauma or acute cerebral infarction to reduce intracranial pressure. Intracranial subdural grid monitoring is used as a diagnostic technique in patients with intractable partial epilepsy to identify an epileptogenic focus for surgical intervention, which also requires the removal of a bone flap from a patient. In some patients surgical removal of a cranial bone flap is necessary to provide access to a tumor or an aneurysm. Immediately following such surgeries, particularly in decompressive craniectomies, the surgical defect may be left open for some period of time, in order to permit swelling and inflammation of brain tissue to recede. The wound may be temporarily covered by a helmet and/or bandages as the patient recovers.
However at some time after such surgical procedures (i.e., decompressive craniectomy, or intracranial electroencephalography, among others) in which bone is explanted from a patient's skull, it becomes necessary for a surgeon to provide a structural replacement that will act as a protective barrier for the patient's brain in the long term. Several factors are considered by surgeons when selecting a replacement including: (1) tissue reactions including immunogenic responses, metal toxicities reactions, and others, (2) fit, (3) potential for infection, and (4) aesthetic results. Surgeons may store the patient's own cranial bone flap for future re-implantation, or they may choose from several synthetic replacements (i.e., poly-methyl-methacrylate (PMMA) implants, hydroxyapatite implants, or titanium implants, among others) for reconstruction.
Re-implanting the patient's own bone is considered to be the best option by the majority of surgeons. In contrast to synthetic replacements, which may cause immunological reactions or other tissue reactions, an autologous cranial bone flap does not pose this risk as it is the patient's own tissue. While synthetic replacements may require significant manipulation to create a good fit and to produce a good cosmetic effect, an autologous bone flap matches the contour of the patient's defect and provides a more natural appearance after healing. In fact, synthetic implants have a number of disadvantages: (1) their preparation can be difficult, time-consuming, and expensive, (2) clinical and aesthetic outcomes can be unpredictable, (3) they do not permit osteointegration, (4) resorption of host bone may occur at the implant site requiring additional reconstructive surgery, and (5) immunogenic responses to the synthetic materials are a possibility. The problems associated with synthetic implants are increased, when the defect being repaired is relatively large. Despite their drawbacks, many hospitals still choose synthetic implants, because (1) they do not have the facilities to safely store/process bone flaps, or (2) they view the use of synthetic implants as less likely to result in an infection at the surgical defect. The rate of infection at a surgical defect closed with a patient's re-implanted bone flap can be relatively high (estimates have been placed between 2% and 20%).
Surgeons have tried a variety of methods to minimize the risk of infection associated with the use of autologous bone flaps to close defects, including: ethylene oxide and/or steam sterilization, freezing, boiling in saline, immersion in hydrogen peroxide solution, and storage in the patient by surgical intra-abdominal placement. These methods have met with only limited success. Still further, many surgical facilities do not have access to resources that would permit them to implement methods of treating bone flaps (for example, many facilities do not have freezers dedicated to autograft tissue storage). Also, some of the methods create additional problems or potential liability for the surgical facilities (for example, if tissue freezers are available, they must be properly overseen and maintained to prevent cross-contamination of stored tissues and unintended thawing of the freezer contents; or if intra-abdominal placement is used for storage of a bone flap, the additional surgery may increase the likelihood of surgical complications in the patient).
When an autologous bone flap does become contaminated by an infection, the surgeon is often forced to remove and discard it, and to fashion a synthetic replacement. Alternatively, the surgeon may treat the contaminated bone flap with steam sterilization or in situ antibiotic irrigation. Neither is an ideal solution. For example, in situ antibiotic irrigation involves removing the contaminated bone flap, scrubbing it with povidone-iodine solution, and soaking in a hydrogen peroxide solution, while the wound is debrided. The bone flap is then re-implanted and an irrigation system is installed with it, and antibiotic medications are infused through the system for several days. The in situ antibiotic irrigation requires a complex set-up and treatment regimen, and an extended hospital stay. It is also ineffective in some situations (i.e., where there is sinus involvement, or when the defect is at the skull base, among others), and it has the potential for causing undesirable immunogenic reactions.
Using methods and autografts of the present invention, hospitals may be provided with autologous grafts that are less expensive than synthetic implants, aesthetically and clinically satisfactory, well-fitting and easy to use, and safe.